Solid oxide fuel cell and cell module comprising same

ABSTRACT

The present specification relates to a solid oxide fuel cell and a cell module including the same.

TECHNICAL FIELD

This application claims priority to and the benefits of Korean PatentApplication No. 10-2015-0119760, filed with the Korean IntellectualProperty Office on Aug. 25, 2015, the entire contents of which areincorporated herein by reference.

The present specification relates to a solid oxide fuel cell and a cellmodule including the same.

BACKGROUND ART

With recent predictions about the exhaustion of existing energyresources such as petroleum and coal, interests in alternative energycapable of replacing these have been growing. As one of such alternativeenergy, fuel cells have received particular attention with advantages ofbeing highly efficient, not emitting pollutants such as NOx and SOx, andhaving sufficient fuel to use.

Fuel cells are a power generating system converting chemical reactionenergy of fuel and oxidizer to electric energy, and hydrogen, methanoland hydrocarbon such as butane are used as the fuel, and oxygen istypically used as the oxidizer.

Fuel cells include polymer electrolyte membrane-type fuel cells (PEMFC),direct methanol-type fuel cells (DMFC), phosphoric acid-type fuel cells(PAFC), alkaline-type fuel cells (AFC), molten carbonate-type fuel cells(MCFC), solid oxide-type fuel cells (SOFC) and the like.

FIG. 1 is a diagram schematically showing a principle of electricitygeneration of a solid oxide-type fuel cell, and the solid oxide-typefuel cell is formed with an electrolyte layer, and a fuel electrode(anode) and an air electrode (cathode) formed on both surfaces of thiselectrolyte layer. When referring to FIG. 1 showing a principle ofelectricity generation of a solid oxide-type fuel cell, air iselectrochemically reduced in an air electrode to produce oxygen ions,and the produced oxygen ions are transferred to a fuel electrode throughan electrolyte layer. In the fuel electrode, fuel such as hydrogen,methanol and butane is injected, and the fuel releases electrons whilebonding to the oxygen ions and electrochemically oxidized to producewater. Through such a reaction, electrons migrate to an externalcircuit.

DISCLOSURE Technical Problem

The present specification is directed to providing a solid oxide fuelcell and a cell module including the same.

Technical Solution

One embodiment of the present specification provides an electrolytesupport-type solid oxide fuel cell including a fuel electrode, anelectrolyte support and an air electrode provided in a consecutiveorder, wherein the electrolyte support includes a gadolinium-dopedceria-based electrolyte layer and a yttria-stabilized zirconia-basedelectrolyte layer each provided on both surfaces of the gadolinium-dopedceria-based electrolyte layer.

Another embodiment of the present specification provides a cell moduleincluding the solid oxide fuel cell as a unit cell.

Advantageous Effects

A solid oxide fuel cell according to one embodiment of the presentspecification has an advantage of high chemical stability.

A solid oxide fuel cell according to one embodiment of the presentspecification has an advantage of high open circuit voltage.

An electrolyte layer of a solid oxide fuel cell according to oneembodiment of the present specification has high ion conductivity.

A solid oxide fuel cell according to one embodiment of the presentspecification has high driving efficiency and favorable long-termstability.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing a principle of electricitygeneration of a solid oxide fuel cell (SOFC).

FIG. 2 is a structural diagram of a vertical section of a solid oxidefuel cell according to one embodiment of the present specification.

FIG. 3 is a SEM image of Example 1.

FIG. 4 is a SEM image of Comparative Example 1.

FIG. 5 is a SEM image of Comparative Example 2.

FIG. 6 is a graph measuring an open circuit voltage (OCV) of Example 1and Comparative Examples 1 and 2.

REFERENCE NUMERAL

100: Fuel Electrode

200: Electrolyte Layer

210: Gadolinium-Doped Ceria-Based Electrolyte Layer

220: Yttria-Stabilized Zirconia-Based First Electrolyte Layer

230: Yttria-Stabilized Zirconia-Based Second Electrolyte Layer

300: Air Electrode

MODE FOR DISCLOSURE

Hereinafter, the present specification will be described in detail.

One embodiment of the present specification provides a solid oxide fuelcell including a fuel electrode, an electrolyte layer and an airelectrode provided in a consecutive order.

The solid oxide fuel cell is preferably an electrolyte support-typesolid oxide fuel cell including an electrolyte layer support having arelatively thicker electrolyte layer compared to other layers.

The fuel electrode may include an oxygen ion conducting first inorganicsubstance, and in the fuel electrode, the oxygen ion conducting firstinorganic substance is present in a crystalline state with the oxygenion conducting first inorganic substance particles being sintered, andthe fuel electrode may be porous having pores so as to inject fuel anddischarge produced water.

The first inorganic substance is not particularly limited as long as ithas oxygen ion conductivity, however, the first inorganic substance mayinclude at least one of yttria-stabilized zirconia (YSZ:(Y₂O₃)_(x)(ZrO₂)_(1-x), x=0.05 to 0.15), scandia-stabilized zirconia(ScSZ: (Sc₂O₃)x(ZrO₂)_(1-x), x=0.05 to 0.15), samarium-doped ceria (SDC:(Sm₂O₃)x(CeO₂)_(1-x), x=0.02 to 0.4), gadolinium-doped ceria (GDC:(Gd₂O₃)x(CeO₂)_(1-x), x=0.02 to 0.4), lanthanum strontium manganeseoxide (LSM), lanthanum strontium cobalt ferrite (LSCF), lanthanumstrontium nickel ferrite (LSNF), lanthanum calcium nickel ferrite(LCNF), lanthanum strontium cobalt oxide (LSC), gadolinium strontiumcobalt oxide (GSC), lanthanum strontium ferrite (LSF), samariumstrontium cobalt oxide (SSC), barium strontium cobalt ferrite (BSCF) andlanthanum strontium gallium magnesium oxide (LSGM).

The fuel electrode may include the same inorganic substance as theelectrolyte layer, and specifically, the first inorganic substance ofthe fuel electrode may include at least one of yttria-stabilizedzirconia (YSZ: (Y₂O₃)_(x)(ZrO₂)_(1-x), x=0.05 to 0.15) andgadolinium-doped ceria (GDC: (Gd₂O₃)x(CeO₂)_(1-x), x=0.02 to 0.4).

The fuel electrode may further include NiO.

The fuel electrode may be prepared by sintering a green sheet preparedwith fuel electrode slurry, or may be prepared by directly coating fuelelectrode slurry, and then drying and sintering the result. Herein, thegreen sheet means, instead of a complete final product, a membrane in afilm form processible in a next step. In other words, the green sheet isobtained by coating with a coating composition including inorganicsubstance particles and a solvent and drying the result to a sheet form,and the green sheet refers to a sheet in a semi-dried state capable ofmaintaining a sheet form while including some quantity of solvent.

The fuel electrode slurry includes the first inorganic substanceparticles, and may further include a binder resin, a plasticizer, adispersant and a solvent. The binder resin, the plasticizer, thedispersant and the solvent are not particularly limited, and commonmaterials known in the art may be used.

The fuel electrode may have a thickness of greater than or equal to 10μm and less than or equal to 100 μm. Specifically, the fuel electrodemay have a thickness of greater than or equal to 20 μm and less than orequal to 50 μm.

The fuel electrode may have porosity of greater than or equal to 20% andless than or equal to 60%. Specifically, the fuel electrode may haveporosity of greater than or equal to 30% and less than or equal to 50%.

The fuel electrode may have pore diameters of greater than or equal to0.1 μm and less than or equal to 10 μm. Specifically, the fuel electrodemay have pore diameters of greater than or equal to 0.5 μm and less thanor equal to 5 μm. More specifically, the fuel electrode may have porediameters of greater than or equal to 0.5 μm and less than or equal to 2μm.

The electrolyte layer may be an electrolyte layer support that isrelatively thicker compared to other layers, and the electrolyte layermay be a multilayer electrolyte layer formed with a multilayer of threeor more layers.

The electrolyte layer may include a gadolinium-doped ceria-basedelectrolyte layer and a yttria-stabilized zirconia-based electrolytelayer each provided on both surfaces of the gadolinium-doped ceria-basedelectrolyte layer. Specifically, the electrolyte layer may include agadolinium-doped ceria-based electrolyte layer, a yttria-stabilizedzirconia-based first electrolyte layer provided on one surface of thegadolinium-doped ceria-based electrolyte layer, and a yttria-stabilizedzirconia-based second electrolyte layer provided on the other surface ofthe gadolinium-doped ceria-based electrolyte layer.

The electrolyte layer may consist of a gadolinium-doped ceria-basedelectrolyte layer and a yttria-stabilized zirconia-based electrolytelayer each provided on both surfaces of the gadolinium-doped ceria-basedelectrolyte layer. Specifically, the electrolyte layer may consist of agadolinium-doped ceria-based electrolyte layer, a yttria-stabilizedzirconia-based first electrolyte layer provided on one surface of thegadolinium-doped ceria-based electrolyte layer, and a yttria-stabilizedzirconia-based second electrolyte layer provided on the other surface ofthe gadolinium-doped ceria-based electrolyte layer.

The gadolinium-doped ceria-based electrolyte layer has high oxygen ionconductivity but has low chemical stability, and open circuit voltagecharacteristics are not favorable. As a result, cell efficiencydecreases and long-term stability is not favorable.

The yttria-stabilized zirconia-based electrolyte layer has high chemicalstability but has low oxygen ion conductivity.

In one embodiment of the present specification, the thickness of theelectrolyte layer increases when the electrolyte layer is used as asupport, which increases resistance of the electrolyte layer. Therefore,while using a gadolinium-doped ceria-based electrolyte layer having highoxygen ion conductivity as a main electrolyte layer, relatively thinyttria-stabilized zirconia-based electrolyte layer is formed on bothsurfaces of the gadolinium-doped ceria-based electrolyte layer tocompensate chemical stability of the gadolinium-doped ceria-basedelectrolyte layer.

A thickness ratio of the gadolinium-doped ceria-based electrolyte layer:the one yttria-stabilized zirconia-based electrolyte layer may begreater than or equal to 1:0.001 and less than or equal to 1:0.1.Specifically, a thickness ratio of the gadolinium-doped ceria-basedelectrolyte layer: the one yttria-stabilized zirconia-based electrolytelayer may be greater than or equal to 1:0.005 and less than or equal to1:0.05.

A ratio of the thickness of the gadolinium-doped ceria-based electrolytelayer: the total thickness of the yttria-stabilized zirconia-basedelectrolyte layers may be greater than or equal to 1:0.002 and less thanor equal to 1:0.2. Specifically, a ratio of the thickness of thegadolinium-doped ceria-based electrolyte layer: the total thickness ofthe yttria-stabilized zirconia-based electrolyte layers may be greaterthan or equal to 1:0.01 and less than or equal to 1:0.1.

The gadolinium-doped ceria-based electrolyte layer may include(Gd₂O₃)_(x)(CeO₂)_(1-x) (x=0.02 to 0.4).

The gadolinium-doped ceria-based electrolyte layer may have a thicknessof greater than or equal to 500 μm and less than or equal to 1000 μm,and this is advantageous in that ion conductivity and mechanicalstrength of a fuel cell are proper. The thickness being less than 500 μmmakes it difficult to physically support a fuel cell, and when thethickness is greater than 1000 μm, resistance increases making itdifficult to accomplish battery cell performance.

Specifically, the gadolinium-doped ceria-based electrolyte layer mayhave a thickness of greater than or equal to 500 μm and less than orequal to 700 μm, and the gadolinium-doped ceria-based electrolyte layermay have a thickness of greater than or equal to 550 μm and less than orequal to 650 μm.

The yttria-stabilized zirconia-based electrolyte layers may each include(Y₂O₃)_(x)(ZrO₂)_(1-x) (x=0.05 to 0.15). Specifically, theyttria-stabilized zirconia-based first electrolyte layer and theyttria-stabilized zirconia-based second electrolyte layer may includethe same or different yttria-stabilized zirconia.

The yttria-stabilized zirconia-based electrolyte layers may each have athickness of greater than or equal to 5 μm and less than or equal to 20μm. This is advantageous in that chemical stability of thegadolinium-doped ceria-based electrolyte layer is compensated whilemaintaining ion conductivity of the electrolyte layer.

Specifically, the yttria-stabilized zirconia-based electrolyte layersmay each have a thickness of greater than or equal to 5 μm and less thanor equal to 10 μm.

The air electrode may include an oxygen ion conducting second inorganicsubstance, and in the air electrode, the oxygen ion conducting secondinorganic substance is present in a crystalline state with the oxygenion conducting second inorganic substance particles being sintered, andthe air electrode may be porous having pores so as to inject air.

The second inorganic substance is not particularly limited as long as ithas oxygen ion conductivity, however, the second inorganic substance mayinclude at least one of yttria-stabilized zirconia (YSZ:(Y₂O₃)_(x)(ZrO₂)_(1-x), x=0.05 to 0.15), scandia-stabilized zirconia(ScSZ: (Sc₂O₃)x(ZrO₂)_(1-x), x=0.05 to 0.15), samarium-doped ceria (SDC:(Sm₂O₃)x(CeO₂)_(1-x), x=0.02 to 0.4), gadolinium-doped ceria (GDC:(Gd₂O₃)x(CeO₂)_(1-x), x=0.02 to 0.4), lanthanum strontium manganeseoxide (LSM), lanthanum strontium cobalt ferrite (LSCF), lanthanumstrontium nickel ferrite (LSNF), lanthanum calcium nickel ferrite(LCNF), lanthanum strontium cobalt oxide (LSC), gadolinium strontiumcobalt oxide (GSC), lanthanum strontium ferrite (LSF), samariumstrontium cobalt oxide (SSC), barium strontium cobalt ferrite (BSCF) andlanthanum strontium gallium magnesium oxide (LSGM).

The air electrode may be prepared by sintering a green sheet preparedwith air electrode slurry, or prepared by directly coating fuelelectrode slurry, and then drying and sintering the result.

The air electrode slurry includes the second inorganic substanceparticles, and may further include a binder resin, a plasticizer, adispersant and a solvent. The binder resin, the plasticizer, thedispersant and the solvent are not particularly limited, and commonmaterials known in the art may be used.

The air electrode may have a thickness of greater than or equal to 10 μmand less than or equal to 100 μm. Specifically, the air electrode mayhave a thickness of greater than or equal to 20 μm and less than orequal to 50 μm.

The air electrode may have porosity of greater than or equal to 20% andless than or equal to 60%. Specifically, the air electrode may haveporosity of greater than or equal to 30% and less than or equal to 50%.

The air electrode may have pore diameters of greater than or equal to0.1 μm and less than or equal to 10 μm. Specifically, the air electrodemay have pore diameters of greater than or equal to 0.5 μm and less thanor equal to 5 μm. More specifically, the air electrode may have porediameters of greater than or equal to 0.5 μm and less than or equal to 2μm.

Another embodiment of the present specification provides a cell moduleincluding the solid oxide fuel cell as a unit cell.

The cell module may include a stack including a unit cell including thesolid oxide fuel cell and a separator provided between the unit cells; afuel supply unit supplying fuel to the stack; and an oxidizer supplyunit supplying an oxidizer to the stack.

The cell module may specifically be used as a power supply of electricvehicles, hybrid electric vehicles, plug-in hybrid electric vehicles orpower storage devices.

Hereinafter, the present specification will be described in more detailwith reference to examples. However, the following examples are forillustrative purposes only, and the scope of the present specificationis not limited thereto.

EXAMPLE Example 1

1. Preparation of GDC Electrolyte Support

1 g of GDC powder (Rhodia, ULSA) was placed in a mold with a 15 mmdiameter, and was uniaxial pressurized with 5 ton for 90 seconds toprepare a pellet, and the pellet was sintered for 3 hours at 1500° C. toprepare a GDC electrolyte support having a thickness of approximately600 μm.

2. Preparation of Auxiliary Electrolyte Slurry

Auxiliary electrolyte slurry was prepared by mixing, based on the totalweight of the auxiliary electrolyte slurry, 50 weight % of YSZ, 10weight % of a dispersant, 0.5 weight % of a plasticizer and 10 weight %of an acryl-based binder with a residual quantity of solvent (29.5weight %).

3. Preparation and Lamination (Coating) of Auxiliary Electrolyte Tape

The prepared auxiliary electrolyte slurry was coated using a doctorblade to prepare a green sheet. The green sheet was laminated on bothsurfaces of the GDC electrolyte support sintered in a pellet form usinga laminator, and the result was sintered for 3 hours at 1350° C. A finalsample having a YSZ auxiliary electrolyte layer having a thickness ofapproximately 7 μm provided on both surfaces of the GDC electrolytesupport was prepared.

[Comparative Example 1]

Preparation was carried out in the same manner as in Example 1 exceptthat a final sample was prepared using only the GDC electrolyte supportof Example 1 without the auxiliary electrolyte.

[Comparative Example 2]

Preparation was carried out in the same manner as in Example 1 exceptthat a final sample was prepared by forming a single auxiliaryelectrolyte layer having a thickness of approximately 7 μm only on thefuel electrode side of the GDC electrolyte support of Example 1.

[Experimental Example 1]

Vertical sections of Example 1 and Comparative Examples 1 and 2 wereobserved using a scanning electron microscope (SEM), and each image isshown in FIG. 3 to FIG. 5.

[Experimental Example 2]

A platinum mesh was formed using a platinum paste, and an electrode wasformed on both surfaces of the sample by sintering the platinum mesh for2 hours at 1000° C. In order to check an open circuit voltage (OCV), avoltage difference was measured while injecting hydrogen on one side,and air on the other side.

For Example 1 and Comparative Examples 1 and 2, the open circuit voltage(OCV) was measured depending on temperatures, and the results are shownin FIG. 6.

The sample using the auxiliary electrolyte (YSZ) on both surfaces[Example 1] had enhanced chemical stability and exhibited a high OCVcompared to the electrolyte support (GDC) without the auxiliaryelectrolyte [Comparative Example 1]. In the sample using the auxiliaryelectrolyte on only one surface in the fuel electrode direction[Comparative Example 2], a slightly increased OCV was obtained, however,the sample was not stabilized as the sample using the auxiliaryelectrolyte on both surfaces.

The invention claimed is:
 1. An electrolyte support-type solid oxidefuel cell comprising: a fuel electrode; an electrolyte support; and anair electrode provided in a consecutive order, wherein the electrolytesupport includes a gadolinium-doped ceria-based electrolyte layer and ayttria-stabilized zirconia-based electrolyte layer each provided on bothsurfaces of the gadolinium-doped ceria-based electrolyte layer, whereinthe yttria-stabilized zirconia-based electrolyte layers each have athickness of 5 μm or more and 20 μm or less, wherein thegadolinium-doped ceria-based electrolyte layer has a thickness of 500 μmor more and 1000 μm or less, and wherein a thickness ratio of thegadolinium-doped ceria-based electrolyte layer: the oneyttria-stabilized zirconia-based electrolyte layer is 1: 0.001 or moreand 1: 0.1 or less.
 2. The electrolyte support-type solid oxide fuelcell of claim 1, wherein the gadolinium-doped ceria-based electrolytelayer includes (Gd₂O₃)_(x)(CeO₂)_(1-x)(x=0.02 to 0.4).
 3. Theelectrolyte support-type solid oxide fuel cell of claim 1, wherein theyttria-stabilized zirconia-based electrolyte layers each include(Y₂O₃)_(x)(ZrO₂)_(1-x)(x=0.05 to 0.15).
 4. A cell module comprising thesolid oxide fuel cell of claim 1 as a unit cell.